Microbial bioavailability regulates organic matter preservation in marine sediments
- 1Geochemistry, Faculty of Geosciences, Utrecht University, P.O. Box 80.021, 3508 TA Utrecht, the Netherlands
- 2Department of Ecosystem Studies, Royal Netherlands Institute for Sea Research-Yerseke, Korringaweg 7, 4401 NT Yerseke, the Netherlands
- 3Center for Isotope Research, Groningen University, Nijenborgh 4, 9747 AG Groningen, the Netherlands
- 4Alfred Wegener Institut for Polar and Marine Research, Bremerhaven, Germany
Abstract. Burial of organic matter (OM) plays an important role in marine sediments, linking the short-term, biological carbon cycle with the long-term, geological subsurface cycle. It is well established that low-oxygen conditions promote organic carbon burial in marine sediments. However, the mechanism remains enigmatic. Here we report biochemical quality, microbial degradability, OM preservation and accumulation along an oxygen gradient in the Indian Ocean. Our results show that more OM, with biochemically higher quality, accumulates under low oxygen conditions. Nevertheless, microbial degradability does not correlate with the biochemical quality of OM. This decoupling of OM biochemical quality and microbial degradability, or bioavailability, violates the ruling paradigm that higher quality implies higher microbial processing. The inhibition of bacterial OM remineralisation may play an important role in the burial of organic matter in marine sediments and formation of oil source rocks.